Add synthesizer (#8)
* Add basic synth
* Ajust synth volume
* Add basic synth popover
* Ajust synth volume
* Add envelope graph
* Update snapshot
* Fix snapshot
* Polish synth setting layout
* Fix graph logic
* Fix erros on the front end
* Fix test
* Improve accesibility
* Improve accesibility
* Improve accesibility
* Update snapshots
* Update screenshot
* Update readme
* Fix some keyboard events
* Ajust synth volumes
* Fix e2e test
* Update version
* Fix: Duplicate script loading on the front end
* Update readme
* Remove comment lines
* Some minor fixes
* Add some comments fix
* Some minro fixes
* Some minro fixes
